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(1) Field of the Invention
This invention relates to foundry binder systems, which will cure in the presence of sulfur dioxide and a free radical initiator, comprising (a) an epoxy resin; (b) an acrylate; (c) an alkyl silicate; and (d) an effective amount of a free radical initiator. The foundry binder systems are used for making foundry mixes. The foundry mixes are used to make foundry shapes (such as cores and molds) which are used to make metal castings, particularly ferrous castings.
(2) Description of the Related Art
In the foundry industry, one of the procedures used for making metal parts is xe2x80x9csand castingxe2x80x9d. In sand casting, disposable molds and cores are fabricated with a mixture of sand and an organic or inorganic binder. The foundry shapes are arranged in core/mold assembly, which results in a cavity into which molten metal will be poured. After the molten metal is poured into the assembly of molds and cores and cools, the metal part formed by the process is removed from the assembly. The binder is needed so the molds and cores will not disintegrate when they come into contact with the molten metal.
Two of the prominent fabrication processes used in sand casting are the no-bake and the cold-box processes. In the no-bake process, a liquid curing catalyst is mixed with an aggregate and binder to form a foundry mix before shaping the mixture in a pattern. The foundry mix is shaped by putting it into a pattern and allowing it to cure until it is self-supporting and can be handled. In the cold-box process, a gaseous curing catalyst is passed through a shaped mixture (usually in a corebox) of the aggregate and binder to cure the mixture.
A cold-box process widely used in the foundry industry for making cores and molds is the xe2x80x9cSO2 cured epoxy/acrylate systemxe2x80x9d. In this process, a mixture of a hydroperoxide (usually cumene hydroperoxide), an epoxy resin, a multifunctional acrylate, typically a coupling agent, and optional diluents, are mixed into an aggregate (sand) and compacted into a specific shape, typically a core or mold. Sulfur dioxide (SO2), optionally diluted with nitrogen or another inert gas, is blown into the binder/aggregate shape. The shape is instantaneously hardened and can be used immediately in a foundry core/mold system.
This system is currently sold by Ashland Specialty Chemical Division, a Division of Ashland Inc., under the trademark of ISOSET(copyright) and has been in use approximately 18 years. About ninety percent of these binders typically use bisphenol-A epoxy resin or bisphenol-F epoxy resin as the epoxy resin component. The multifunctional acrylate most commonly used is trimethylolpropane triacrylate. The hydroperoxide most commonly used is cumene hydroperoxide.
Though the process has been used successfully in many foundries, one of the major weaknesses of the system has been the erosion resistance of foundry shapes made with the binder. Erosion occurs when molten metal contacts the mold or core surfaces during the pouring process and the sand is dislodged at the point of contact. This occurs because the binder does not have sufficient heat resistance to maintain surface integrity until the pouring process is complete. The results is that sand, which has eroded from the foundry shape, is carried into the metal casting, creating weak areas in the casting. A dimensional defect is also created on the surface of the casting.
To correct this problem, foundries have historically resorted to coating the foundry shape with a refractory coating to prevent erosion. Thus, core and mold assemblies are dipped into or sprayed with a slurry composed of a high melting refractory oxide, a carrier such as water or alcohol, and thixotropic additives. When dried on a mold/core surface, the coating very effectively prevents erosion, in most cases. The problem with this approach is that the coating operation is messy, requires expensive gas fired, microwave, or radiant energy ovens to dry the wash onto the core surface. When the core/molds are heated during the drying process the strength of the organic binder to aggregate bond weakens significantly. This results in problems with handling the hot cores and reduction in productivity due to core distortion or cracking. This is especially true with microwave drying.
The subject invention relates to foundry binder systems, which cure in the presence of gaseous sulfur dioxide and a free radical initiator, comprising:
(a) 20 to 70 parts by weight of an epoxy resin;
(b) 5 to 50 parts by weight of an acrylate;
(c) 1 to 20 parts by weight of an alkyl silicate; and
(d) an effective amount of a hydroperoxide,
where (a), (b), (c), and (d) are separate components or mixed with another of said components, provided (b) is not mixed with (d), and where said parts by weight are based upon 100 parts of binder.
It has been found that addition of the alkyl silicate the binder system results in or molds with enhanced hot tensile strengths, enhanced hot impact resistance, and/or enhanced hot strength properties, which is reflected in improved erosion resistance. These improvements result in better castings and fewer casting defects when the foundry shapes are used to make metal castings. These improvements are even more noticeable if a phenolic resin is added to the binder system.
In particular, foundry shapes made from binders based on epoxy novolac resins, bisphenol-F epoxy resins, or mixtures of bisphenol-F/epoxy novolac resins show enhanced erosion resistance. On the other hand, foundry shapes made with binders based on bisphenol-A epoxy resins exhibit improved hot tensile strength and hot impact resistance, which is particularly significant when the foundry shapes are coated with an aqueous refractory coating and oven-dried.
The foundry binders are used for making foundry mixes. The foundry mixes are used to make foundry shapes, such as cores and molds, which are used to make metal castings.
Not Applicable.
The detailed description and examples will illustrate specific embodiments of the invention will enable one skilled in the art to practice the invention, including the best mode. It is contemplated that many equivalent embodiments of the invention will be operable besides these specifically disclosed. All percentages are percentages by weight unless otherwise specified.
An epoxy resin is a resin having an epoxide group, i.e., 
such that the epoxide functionality of the epoxy resin (epoxide groups per molecule) is equal to or greater than 1.9, typically from 2.0 to 4.0.
Examples of epoxy resins include (1) diglycidyl ethers of bisphenol A, B, F, G and H, (2) halogen-substituted aliphatic epoxides and diglycidyl ethers of other bisphenol compounds such as bisphenol A, B, F, G, and H, and (3) epoxy novolacs, which are glycidyl ethers of phenolic-aldehyde novolacs, (4) mixtures thereof.
Epoxy resins (1) are made by reacting epichlorohydrin with the bisphenol compound in the presence of an alkaline catalyst. By controlling the operating conditions and varying the ratio of epichlorohydrin to bisphenol compound, products of different molecular weight can be made. Epoxy resins of the type described above based on various bisphenols are available from a wide variety of commercial sources.
Examples of epoxy resins (2) include halogen-substituted aliphatic epoxides, diglycidyl ethers of other bisphenol compounds such as bisphenol A, B, F, G, and H, and epoxy novolac resins. Examples of halogen-substituted aliphatic epoxides include epichlorohydrin, 4-chloro-1,2-epoxybutane, 5-bromo-1,2-epoxypentane, 6-chloro-1,3-epoxyhexane and the like.
Examples of epoxy novolacs (3) include epoxy cresol and epoxy phenol novolacs, which are produced by reacting a novolac resin (usually formed by the reaction of orthocresol or phenol and formaldehyde) with epichlorohydrin, 4-chloro- 1,2-epoxybutane, 5-bromo-1,2-epoxypentane, 6-chloro-1,3-epoxyhexane and the like.
Preferably used are epoxy resins having an average epoxide functionality of at least 2.1 to 3.5, preferably from about 2.3 to about 3.0. Particularly preferred are epoxy novolacs having an average weight per epoxy group of 165 to 200.
The acrylate is a reactive acrylic monomer, polymer, or mixture thereof and contains ethylenically unsaturated bonds. Examples of such materials include a variety of monofunctional, difunctional, trifunctional, tetrafunctional and pentafunctional monomeric acrylates and methacrylates. A representative listing of these monomers includes alkyl acrylates, acrylated epoxy resins, cyanoalkyl acrylates, alkyl methacrylates, cyanoalkyl methacrylates, and difunctional monomeric acrylates. Other acrylates, which can be used, include trimethylolpropane triacrylate, pentaerythritol tertraacrylate, methacrylic acid and 2-ethylhexyl methacrylate. Typical reactive unsaturated acrylic polymers, which may also be used include epoxy acrylate reaction products, polyester/urethane/acrylate reaction products, acrylated urethane oligomers, polyether acrylates, polyester acrylates, and acrylated epoxy resins.
The alkyl silicates used in the binder may be monomeric or polymeric alkyl silicates. Examples of monomeric alkyl silicates include tetraethyl orthosilicate, tetramethyl orthosilicate, and mixed alkyl silicates. Examples of polymeric alkyl silicates include oligomers of alkyl silicates, such as Dynasil 40, oligomers of alkoxy trialkoxysilanes, oligomers of dialkyl dialkoxysilanes, such as Silbond 40, and oligomers of trialkyl monoalkoxysilanes. Preferably used are tetraethyl orthosilicate and polyethylsilicate. The free radical initiator is a peroxide and/or hydroperoxide. Examples include ketone peroxides, peroxy ester free radical initiators, alkyl oxides, chlorates, perchlorates, and perbenzoates. Preferably, however, the free radical initiator is a hydroperoxide or a mixture of peroxide and hydroperoxide. Hydroperoxides particularly preferred in the invention include t-butyl hydroperoxide, cumene hydroperoxide, paramenthane hydroperoxide, etc. The organic peroxides may be aromatic or alkyl peroxides. Examples of useful diacyl peroxides include benzoyl peroxide, lauroyl peroxide and decanoyl peroxide. Examples of alkyl peroxides include dicumyl peroxide and di-t-butyl peroxide.
Cumene hydroperoxide and/or a multifunctional acrylate, such as trimethylolpropane triacrylate, may be added to the epoxy novolac resin before mixing it with the foundry aggregate. Optionally, a solvent or solvents may be added to reduce system viscosity or impart other properties to the binder system such as humidity resistance. Examples of solvents include aromatic hydrocarbon solvents, such as such as o-cresol, benzene, toluene, xylene, ethylbenzene, alkylated biphenyls and naphthalenes; reactive epoxide diluents, such as glycidyl ether; or an ester solvent, such as dioctyl adipate, esters derived from natural oils, e.g. butyl tallate, rapeseed methyl ester, and the like, or mixtures thereof. If a solvent is used, sufficient solvent should be used so that the resulting viscosity of the epoxy resin component is less than 1,000 centipoise, preferably less than 400 centipoise. Generally, however, the total amount of solvent is used in an amount of 0 to 25 weight percent based upon the total weight of the epoxy resin.
Although solvents are not required for the reactive diluent, they may be used. Typical solvents used are generally polar solvents, such as liquid dialkyl esters, e.g. dialkyl phthalate of the type disclosed in U.S. Pat. No. 3,905,934, and other dialkyl esters such as dimethyl glutarate, dimethyl succinate, dimethyl adipate, and mixtures thereof. Esters of fatty acids, particularly rapeseed methyl ester and butyl tallate, are also useful solvents. Suitable aromatic solvents are benzene, toluene, xylene, ethylbenzene, and mixtures thereof. Preferred aromatic solvents are mixed solvents that have an aromatic content of at least 90% and a boiling point range of 138xc2x0 C. to 232xc2x0 C. Suitable aliphatic solvents include kerosene. Although the components can be added to the foundry aggregate separately, it is preferable to package the epoxy novolac resin and free radical initiator as a Part I and add to the foundry aggregate first. Then the ethylenically unsaturated material, as the Part II, either alone or along with some of the epoxy resin, is added to the foundry aggregate.
Phenolic resins may also be used in the foundry binder. Examples include any phenolic resin, which is soluble in the epoxy resin and acrylate, including based catalyzed phenolic resole resins and novolac resins. However, if phenolic resins are used in the binder, typically used are phenolic resole resins known as benzylic ether phenolic resole resins, including alkoxy-modified benzylic ether phenolic resole resins. Benzylic ether phenolic resole resins are prepared by reacting an excess of aldehyde with a phenol in the presence of a divalent metal catalyst. Benzylic ether phenolic resole resins, or alkoxylated versions thereof, are well known in the art, and are specifically described in U.S. Pat. Nos. 3,485,797 and 4,546,124, which are hereby incorporated by reference. These resins contain a preponderance of bridges joining the phenolic nuclei of the polymer, which are ortho-ortho benzylic ether bridges. They are prepared by reacting an aldehyde and a phenol in a mole ratio of aldehyde to phenol of at least 1:1 in the presence of a metal ion catalyst, preferably a divalent metal ion such as zinc, lead, manganese, copper, tin, magnesium, cobalt, calcium, and barium.
It will be apparent to those skilled in the art that other additives such as silanes, silicones, release agents, defoamers, wetting agents, etc. can be added to the aggregate, or foundry mix. The particular additives chosen will depend upon the specific purposes of the formulator.
Typically, the amounts of the components used in the binder system are from 20 to weight percent of epoxy resin, preferably from 35 to 60 weight percent; 5 to 50 weight percent of multifunctional acrylate, preferably from 15 to 35 weight percent; from 1 to 20 parts of alkyl silicate, preferably from 5 to 15 weight percent; from 10 to 25 weight percent of free radical initiator, preferably from 15 to 20 weight percent; and optionally from 2 to 20 parts of phenolic resin, preferably from 6 to 12 weight percent, where the weight percent is based upon 100 parts of the binder system.
Various types of aggregate and amounts of binder are used to prepare foundry mixes by methods well known in the art. Ordinary shapes, shapes for precision casting, and refractory shapes can be prepared by using the binder systems and proper aggregate. The amount of binder and the type of aggregate used are known to those skilled in the art. The preferred aggregate employed for preparing foundry mixes is sand wherein at least about 70 weight percent, and preferably at least about 85 weight percent, of the sand is silica. Other suitable aggregate materials for ordinary foundry shapes include zircon, olivine, aluminosilicate, chromite sands, and the like.
In ordinary sand type foundry applications, the amount of binder is generally no greater than about 10% by weight and frequently within the range of about 0.5% to about 7% by weight based upon the weight of the aggregate. Most often, the binder content for ordinary sand foundry shapes ranges from about 0.6% to about 5% by weight based upon the weight of the aggregate in ordinary sand-type foundry shapes.
The foundry mix is molded into the desired shape by ramming, blowing, or other known foundry core and mold making methods. The shape is then cured almost instantaneously by the cold-box process, using vaporous sulfur dioxide as the curing agent (most typically a blend of nitrogen, as a carrier, and sulfur dioxide containing from 35 weight percent to 65 weight percent sulfur dioxide), described in U.S. Pat. Nos. 4,526,219 and 4,518,723, which are hereby incorporated by reference. The shaped article is preferably exposed to effective catalytic amounts of gaseous sulfur dioxide, and, optionally, minor amounts of a carrier gas can be used. The exposure time of the sand mix to the gas is typically from 0.5 to 10 seconds. The foundry shape is cured after gassing with sulfur dioxide. Oven drying is needed if the foundry shape is coated with a refractory coating.
The core and/or mold may be formed into an assembly. When making castings, the assembly is typically coated with a water-based refractory coating and passed through a conventional or microwave oven to remove the water from the coating. The item is then ready to be handled for further processing.
The abbreviations used in the examples are as follows: